1. Field of the Invention
This invention pertains generally to wireless networking, and more particularly to an apparatus and method that provides for automatic switching between different network interfaces in a mobile device so that the mobile device can seamlessly roam among different types of wireless networks.
2. Description of Related Art
In recent years, wireless network interfaces have become extremely important to the functionality of mobile devices. Examples of mobile devices that use wireless networking are laptop computers and personal digital assistants (PDAs). Wireless connectivity of a mobile device to the Internet or to an intranet can increase mobility, convenience and productivity, but there are certain limitations associated with that connectivity. For example, the widely used IEEE 802.11 (WLAN) wireless networking technology provides high bandwidth but is limited in geographical coverage. On the other hand, while cellular technologies such as CDMA/WDCMA/GSM/GPRS (WAN) provide much wider (and even global) geographical coverage, they do so at a much lower bandwidth than 802.11 networking.
Due to the use of different standards and communications protocols for wireless networking, in order to achieve true global coverage it is currently necessary to utilize a combination of several plug-in or integrated connectivity interfaces and to manually switch between interfaces while roaming through different geographical areas or communication sites. For example, a laptop computer or PDA may have an integrated 802.11b interface and one or more PCMCIA or CF-card slots for swappable add-on cards. This allows the user to, for example, select among IEEE 802.11a, IEEE 802.11b, CDMA/WCDMA or GSM/GPRS wireless interface cards. Again, however, the user experiences a degree of inconvenience since it is necessary to manually enable, disable or otherwise switch between the interfaces. For example, the user may have to manually switch from an 802.11 module to a CDMA/WCDMA or GSM/GPRS module if the user moves from 802.11 hot spots to cellular networks. With many operating systems, this also requires the user to close the network connection session and restart it again using the new wireless interface.
Those skilled in the art will appreciate that network communications typically rely on the Open Systems Interconnection (OSI) Reference Model in which there are seven communications layers. Currently, products are available that use OSI Layer 5 to provide proxy-based session level mobility and OSI Layer 3 with Mobile IP to provide network level mobility. However, those products are based on a client/server architecture and roaming connection changes require interactions of both client and server components.
Accordingly, there is a need for seamless roaming capability to be built-in to mobile devices so that different wireless interfaces will automatically be selected while roaming without the need for manual selection and/or restarting the wireless networking session. The present invention satisfies that need as will herein be described.